1. Field of the Invention
This invention is concerned with systems and methods of dispensing precise volumes of fluid in droplet form and of generating very low fluid flow rates.
2. Description of the Related Art
The need to dispense very small volumes of fluid, or to control very low fluid flow rates, routinely arises in chemical and biomedical laboratories, among other places. For example, a type of blood test may require that 5 .mu.L of a blood sample be precisely dispensed onto a slide or plate, or an intravenous medication may need to be provided at a rate expressed in terms of nanoliters or picoliters per second.
Conventionally, such low flow rates and/or dispensed volumes have been provided using a syringe pump to displace a known volume of liquid, and then to provide tubing and/or a needle to route the displaced fluid to its intended destination. This method assumes that the volume displaced by the pump is accurately delivered to the dispensing end of the system. Unfortunately, as the volumes to be controlled become smaller and smaller, significant errors are produced by, for example, the compliance of the tubing, fluids which cling to the needle tip, temperature variations, and inaccuracies in the syringe itself. When the volume needed for a particular purpose can be contained in a single fluid droplet, the accuracy obtainable with such a conventional system is often inadequate.